1. Field of the Invention
This invention relates to an insulation structure of a rotary electrical machinery such as electric motors or electric generators.
Priority is claimed on Japanese Patent Application No. 2006-082474, filed Mar. 24, 2006, the contents of which are incorporated herein by reference.
2. Description of Related Art
In stators of rotary electrical machinery such as electric motors or electric generators, electrical insulation between an iron core and a winding of the stator is needed. For example, in an electric motor of Japanese Unexamined Patent Application, First Publication No. 2001-112205, teeth are electrically insulated from a winding by providing an insulator formed from a hard insulating material (e.g., a resin) at both ends of the axial direction of the teeth of an iron core, providing an insulating paper along the side surface of the teeth crossing the circumferential direction of the teeth, and providing the insulator and the insulating paper so as to be stacked on each other at the end portion thereof along the axial direction.
The electric motors generate heat at the winding by energizing them. Therefore, it is important to radiate the heat efficiently for downsizing and improving the output of the electric motors. For this purpose, radiating heat efficiently from the iron core by transferring the heat generated at the winding to the teeth via a heat-conductive electrical-insulation resin sheet which is used alternatively to the insulating paper is investigated.
FIGS. 9 to 11 show an insulation structure of an electric motor developed prior to the present invention. The stator of the electric motor is constituted from a plurality of stator pieces arranged circularly. FIG. 9 shows a single stator piece 100 before winding. An insulation structure of a combination of a heat-conductive electrical-insulation resin sheet and an insulator is adopted for the stator piece 100. Hereafter, the axial direction of the teeth is the same direction as the axial direction of the stator and conforms to the axial direction of the rotor.
Teeth 102 of an iron core (hereafter, a split iron core) 101 of the stator piece 100 is provided with insulators 110 at both ends along the axial direction. The insulator 110 includes an end wall 111 which is arranged along an axial direction end surface 103 of the teeth 102 and a side wall 112 extending along a side surface 104 of the teeth 102 crossing the circumference direction of the teeth 102. The heat-conductive electrical-insulation resin sheet 120 is arranged so as to cover substantially the whole of the side surface 104 of the teeth 102 along the side surface 104. Axial direction end portions 121 of the heat-conductive electrical-insulation resin sheet 120 are arranged so as to be stacked on the side walls 112 of the insulator 110. A superposition portion 130, which is a stacked combination of the heat-conductive electrical-insulation resin sheet 120 and the insulator 110, is set to a prescribed axial size in order to maintain an insulation range. FIG. 10 shows a cross section of the teeth 102 at the axial middle part. FIG. 11 shows a cross section at the superposition portion 130.
The axial direction end surface 103 of the teeth 102 is electrically insulated from a winding (not illustrated) by the end wall 111 of the insulator 110. The side surfaces 104 of the teeth 102 are electrically insulated from the winding (not illustrated) by the side wall 112 of the insulator 110 and the heat-conductive electrical-insulation resin sheet 120.
The heat-conductive electrical-insulation resin sheet 120 needs to be in contact with the winding in the stator piece 100 for efficiently transferring the heat generated at the winding to the stator piece 100. Therefore, the heat-conductive electrical-insulation resin sheet 120 needs to be thicker than the side wall 112 of the insulator 110.
However, if an end portion 121 of the heat-conductive electrical-insulation resin sheet 120 which is thicker than the side wall 112 of the insulator 110 is stacked on the side wall 112 of the insulator 110, the end portion 121 of the heat-conductive electrical-insulation resin sheet 120 would be elastically compressed by the winding wound thereon, and the side wall 112 of the insulator 110 would be stressed by the reaction force of the compression. The permanence of the insulator 110 is adversely affected by use under stress.
In view of this, a step is formed at the end of the side wall 112 of the insulator 110 in order to thin the side wall 112 at the superposition portion 130 and a step is formed at the end portion 121 of the heat-conductive electrical-insulation resin sheet 120 in order to thin the end portion 121 at the superposition portion 130 so that the thickness of the superposition portion 130 before the winding is wound (i.e., the thickness of the side wall 112 of the insulator 110 and the end portion 121 of the heat-conductive electrical-insulation resin sheet 120) becomes the same as that of the heat-conductive electrical-insulation resin sheet 120 except at the superposition portion 130. Thereby, the deformation volume of the end portion 121 of the heat-conductive electrical-insulation resin sheet 120 is lessened: and the stress applied to the side wall 112 of the insulator 110 can be decreased. However, it is difficult to form the step at the end portion 121 of the heat-conductive electrical-insulation resin sheet 120 since the heat-conductive electrical-insulation resin sheet 120 is comparatively thin.
In addition, a small gap would be unavoidably formed between the side surface 104 and the side wall 112 at the superposition portion 130 since the side wall 112 of the insulator 110 which is in contact with the side surface 104 of the teeth 102 is made from a hard material. As a result, an air layer between the side surface 104 and the side wall 112 is formed, and the heat conduction is deteriorated.